AWWA ACE94122

This paper reports data from a research program whose main objective is to examine the origins and turnover time of dissolved organic carbon (DOC) in various carbon reservoirs in forested watersheds on the Canadian Shield. The approach described involves the use of 13C and 14C, the stable and radioactive isotopes of carbon, respectively. The DOC produced and flushed from the watershed is a mixture of compounds with varying 14C contents depending on the DOC parent material and the residence time of the DOC in the watershed. Tritium data and hydrogeologic studies indicated that the average water residence time of the groundwater in Harp Lake catchment must be less than 35 years. Thus, the 14C content of the DOC reflects the average DOC production and turnover time, because the watershed is being continuously flushed of DOC on a time scale that is essentially instantaneous compared with the 14C half-life. The data reported here make use of carbon isotope data on streams, groundwater and soils and DOC concentration patterns in streams and their link to the hydrology, to provide information about the sources of stream DOC.